Alarm annunciator with independent acknowledgement indication



May 31, 1966 E. s. IDA ETAL 3,254,331

I ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION FiledNov. 20, 1962 7 Sheets-Sheet 1 OCK-IN +s7v. VOLT BUS 57v BUS WGD 22 \JL0 1 I 23 [9 INPUT SIGNAL l5 CIRCUIT RED 20 I6 GREEN I2 25 4 COMMON FIG-lNON LOCK-IN +57 VOLT BUS I0 NPUT 2o EIIGNAL GREEN cIRcuIT FIGZ f fINVENTORS RD 5. IDA RED EDWA BY EDWARD W. YETTER ATTORNEY y 1966 E. s.IDA ETAL 3,254,331

ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION EDWARD W.YETTER ATTORNEY 7 Sheets-Sheet 3 E. S. IDA ETAL ALARM ANNUNCIATOR WITHINDEPENDENT ACKNOWLEDGEMENT INDICATION INVENTORS EDWARD S.IDA EDWARD W.YETTER ATTORNEY mo m @E k 1 m2 Emmi. mw mm Tmw m? jilwo I? b m5 M3202xuwzi n W 5 S w m m D MW H202 wwml m0 no x2325 w j u vm k mam Ema? J mmP S mm 512: Av 6 v F M 5 3 AV 2x54 h. R A Q d W H 1| J aw M3902 9H 2 wan w o\ NP 3 ||||Il||ll|l|| on m V 3 Q 8 8 xuwzE z 5&8 N E on. S L M 4m2 50 8 A YA 6. 26 5 20 Ema,

May 31, 1966 Filed Nov. 20, 1962 y 1966 E. 8. [DA ETAL 3,254,331 T ALARMANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION Filed Nov. 20,1962 '7 Sheets-Sheet 4 +57 VOLT BUS RNGBACK 98 LAMP 78 +150 VOLT BUS TOSECON D BRABCH CIRCUIT RING BACK AUDlBl BUS I23 FLASHER BUS 1 0 F166FIGBA 57 VOLT BUS T Lu +|O5 VOLT BUS ACK. BUS

FIG. 8B

FIG-7 INVENTORS EDWARD S. IDA BY EDWARD W. YETTER 1 T- QWE ATTORNEY May31, 1966 E. s. IDA ETAL ALARM ANNUNCIATOR WITH INDEPENDENTACKNOWLEDGEMENT INDICATION '7 Sheets-Sheet 6 Filed Nov. 20, 1962 mOE AE2 25 51 2 A a SEQ? mom m n W n N: 20228 rll Me R mam o2+ INVENTORSEDWARD S. I DA BY EDWARD W- YETTER 7/ gwcm ATTORNEY y 3 1966 E. s. IDAETAL 3,254,331

ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION Filed Nov.20, 1962 7 Sheets-Sheet 7 COMMON 5 BUS AUDIBLE BUS FLASHER BUS +57 VOLTBUS INVENTORS EDWARD S. IDA EDWARD W. YETTER ATTORNEY United StatesPatent 3,254,331 ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENTINDICATION Edward S. Ida, Folsom, and Edward W. Yetter, West Chester,Pa., assignors to E. I. du Pont de Nemours and Company, Wilmington,Del., a corporation of Delaware Filed Nov. 20, 1962, Ser. No. 238,867 6Claims. (Cl. 340-2132) This invention relates to an alarm annunciator,and particularly to an electrical alarm annunciator which furnishesadditional information regarding the state of the point monitored and,further, which is adapted to either pulse type or steady current alarmsignal actuation.

Modern manufacturing operations require a more or less continuousmonitoring of a multiplicity of operating conditions in rapid sequence,and this has led to a proliferation of independent sensing circuits,each of which is adapted to monitor, or in some instances directlyeffect, aspecific process step. It is imperative that management havepositive assurance at all times as to the moment-bymoment status of eachindividual operating condition as sensed by the associated monitorcircuits, which often total hundreds or even thousands of points, as theindividual circuits are customarily called. Thus, there is a strongrequirement for simplicity in design in order to reduce the highaggregate cost of the annunciators, coupled with extreme reliability inprocess surveillance service.

A convenient method of ascertaining whether a control point is, at anygiven time, in safe or unsafe state is to provide means establishing aunique electrical circuit corresponding to the existing point condition.It is practicable to appraise the status of large numbers of points byrapid, repetitive scanning techniques wherein points are sampled inorderly sequence and a characteristic electrical pulse elicited as thesignal of safe or unsafe status, respectively, US. application Ser. No.108,521, now Patent No. 3,201,572, assigned to the same assignee,teaches a control method and apparatus relying on electrical pulsetransmission as the effective control agency, and it is a simple matterto incorporate in such a device additional circuitry routing a tell-talepulse confirmatory of point status to an annunciator of the design ofthis invention, which is well-adapted to pulse-type operation,'but isstill versatile enough for employment with steady current alarm inputsshould this be desired.

An object ofthis invention is to provide an alarm annunciator capable ofactuation responsive to electrical pulses as well as to steady currentsignals. Another object of this invention is to provide an alarmannunciator capable of furnishing more complete information on monitoredpoint status, such as, for example, instant advice of restoration of apoint to normality. Another object of this invention-is the provisionofan alarm annunciator particularly adapted to the convenient inclusionof auxiliaries providing additional information with respect to theoccurrence of anomalies in the condition monitored, or the indication ofsteps taken corrective of -any anomalies signaled. Other objects of thisinvention Patented May 31, 1966 embodiment of basic non lock-in typeannunciator according to this invention,

FIGS. 3A-3C are schematic representations of the lefthand branches onlyof the embodiments of FIGS. 1 and 2, I

detailing three preferred designs of input circuit each employing adifferent type of alarm signal actuation, FIG. 3A being directed topulse utilization, FIG. 3B to normally closed contact, steady currentutilization and FIG. 3C to normally open contact, steady currentutilization,

FIG. 4 is a schematic representation of another embodiment of thisinvention utilizing a diode as the electronic blocking means in theleft-hand circuit branch instead of the transistors employed in theembodiments of FIGS. 1 and 2, this figure showing two completeindependent annunciators of which the left-hand one is a lock-in designwhereas the right-hand one is a non lock-in design.

FIG. 5 is a schematic representation of a preferred circuit arrangementof audible alarms, acknowledgement pushbuttons, and lamp flasherauxiliaries for the annunciaare to provide an electrical alarmannunciator which is tor of this invention, inter-connection with theannunciator proper being, illustrated with respect to the lock-inembodiment of annunciator shown in FIG. 4,

FIG. 6 is a schematic representation of a preferred embodiment of RingBack auxiliary adapted for use with the lock-in species only of thisinvention, inter-connection with the annunciator proper beingillustrated with re- .spect to the lock-in embodiment of annunciatorshown either the lock-in or non lock-in species of this invention,

interconnection withthe annunciator proper being illustrated withrespect to the left-hand branch of the embodiments of annunciator shownin FIG. 4,

' FIG. 7A is a schematic representation of two individual annunciatorembodiments, one of the lock-in type and the other a non lock-in,complete with First On, Ringback, flasher and audible alarm auxiliaries,

FIGS. 8A and 8B are schematic representations of embodiments of alarmindication and acknowledgement verification branch circuits,respectively, of a lock-in type annunciator wherein neon lamps aresubstituted in a dual capacity for the switching element and alarm lampcollectively of the embodiments of FIGS. 1 and 4, with the points ofpulse signal introduction rearranged to suit the changed polarityrequirements,

FIG. 9 is a schematic representation of two preferred designs of lock-intype annunciatorcircui't utilizing neon lamps as the visual indicatorsand also as switching elements, the left-hand embodiment beingpulse-actuated, whereas the right hand embodiment is steady directcurrent actuated with a switch in normally closed contact state for thesignal input,

FIG. 10 is a schematic representation of yet another embodiment oflock-in type pulse-actuated annunciator utilizing neon lamps and atransistor in the first branch.

circuit thereof, and

ment of alarm indication branch circuit utilizing a switch in normallyopen contact state for the signal input.

Generally, the electrical annunciator of this invention comprises, incombination, a D.-C. supply, a first bnanch circuit and a second branchcircuit connected in parallel circuit relationship one to the otheracross the DC.

supply, the first branch circuit being'provided with an alarm indicationlamp together with alarm indication lamp control means responsive,first, to receipt of a signal signifying the existence of an abnormalstate in a point monitored establishing a distinctive illuminatedstateof .the alarm indication lamp and, second, to receipt or a signalsignifying the restoration of the point monitored by the employment oftwo more or less self-contained circuits, the purpose of the first ofwhich is to handle alarm indications incident to deviation of the pointmonitored from normal behavior, whereas the purpose of the second .is toprovide an acknowledgement verification facility. Such an approach hasvery great advantages over that hitherto followed in annunciator design,because there exist three items of information which must becommunicated, namely: (a) normal condition, (b) alarm (or abnormal)condition and (c) acknowledged condition. If only one lamp is employedfor the entire communication, three states of illumination are requiredas an absolute minimum, whereas, when two'independent lamps are used,only two states of illumination are necessary. The essential electricalcircuitry, especially where solid state components are employed, is muchsimpler and more reliable in the latter case.

Perhaps an even more important advantage of the twolamp system is thefact that, in rapid scanning, mu-ltiplexed monitoring systems, thereexists the ability to accept repetitive information during eachsuccessive soan cycle without disturbance to the sequence of operationof any given annunciator. Thus, the scanning alarm monitor is notrequired to remember that it previously gave an OFF or an ON signal tothe annunci ator, so as to require suppression of later-repeatedsignals.

Referring to 'FIG. 1, there is shown a preferred embodiment of basiclockain type alarm annunciator according to this invention wherein theinput signal circuit is represented simply as a block 10 by way ofexpressing the generality of choice possible in signal input, all ashereinafter described with particular reference to FIGS. 3A to 3C,inclusive.

T-he tannunciator unit, one of which is reserved exclusively to eachpoint monitored, comprises a D.-C. supply represented by leads, 1 1 and:12, of which 11 can typically be la +57 v. lead whereas 12 is agrounded conductor common. Two parallel-connected branch circuits areprovided across leads 1 1 and 12, of which the left-hand one shown inFIG. 1 is referred to in this description and the claims 'as the firstbranch circuit, which is reserved to alarm indication exclusively,whereas the right-hand one is denoted the second branch circuit, whichis reserved to acknowledgement verification exclusively.

The first branch circuit has connected therein, in series electricalarrangement, a current-stable, negative resistance switching elementwhich can typically be, as indicated, a 4-l ayer diode 14 (e.g., a Type4E 40-28, or a IN 3304), a P N-P transistor 15 (typically a MotorolaType 2N398A) as the electronic blocking means and a red alarm indicationlamp 516 (typically, a GB. No. 1835, 55 v., 50 ma. miniature lamp). putsignal to the annunciator is introduced from input signal circuit '10via conductor 18 connected to the base of transistor 15.

The second branch circuit includes a 4-1ayer diode 19 (Type 4 E 8028)similar to diode 114, and a green acknowledgement verification lamp 20,similar to lamp 16. The second branch circuit also incorporates a diode21 (typically a type SR169Z) and is capacitor-coupled to the firstbranch circuit via capacitor 22 (typically 0.01

The negative polarity inmfd. size) and conductor 23, connected on theone hand between diode '14 and transistor #15, and on the other betweendiode 2'1 and diode 19. Finally, there is provided a normally closed,manually-operated switch 25 in circuit between the second branch circuitand D.-C. supply leads 1 1 and 12.

The circuit for the preferred embodiment of the basic non lock-in.annunciator according to this invention, shown in FIG. 2, is identicalin most respects to that described 'for the lock-in embodiment ofFIG. 1. Accordingly, all counterpart elements are therefore denoted bythe same reference numerals, but with -a prime appended. The couplingbetween first and second branch circuits is, in this design, achieved bya capacitor 26 (typically a 0.25 mfd. size) and a conductor 27,connecting, in this embodiment, between transistor and red alarmindication lamp 16 on the one hand, and green acknowledgementverification lamp 20 and diode 19 on the other. It will be noted thatthe relative location of the acknowledgement verification lamp 20 ischanged from that of lamp 20, in that lamp 20 is, in this case,

interposed between diodes 21 and 19, instead of to one side of them.

Before proceeding with a description of the operation of the apparatusesof FIGS. 1 and 2, it is believed desirable to describe the threeprincipal types of signal input which can be conveniently employed withthe annunciator. Thus, FIG. 3A shows a preferred design of signal inputcircuit intended for use with positive and negative electric pulses,such as those hereinbefore referred to with respect to US. applicationSer. No. 108,521. Here it is necessary to utilize a positive polaritytransistor biasing bus 30 (typically +37 v., i.e., less than the +57 v.of supply lead 11) connected through resistors 31 and 32 (each typically3.9K ohms) between which latter the negative polarity 0N pulse signalsignifying the existence of an abnormal state in the point monitored, isintroduced via lead 33, whereas the positive polarity OFF pulse signal,signifying the restoration of the point monitored to normal state, isintroduced via lead 34. Each of these pulses is typically supplied at avoltage level of about :20 v. referred to the +37 v. bus 30.

Another common input is that depicted in FIG. 3B, employing a steadyD.-C. signal drawn from D.-C. supply lead 11 through a normally closedswitch 36' connected to the grounded common 12 via a resistor 37(typically 7.5K ohms). In this construction switch 36 is maintainedclosed via the mechanical connection indicated schematically in brokenline representation at 33 at all times during which the point monitoredis in normal behavior, being open at all other times. As in FIG. 3A apositive polarity biasing signal is imposed on the base element oftransistor 15 via two series-connected resistors 31 and 32 (eachtypically of 3.9K ohms value), :1 capacitor 40 (typically 1 to 10 f.size) being connected midway between resistors 31' and 32 and positivelead 11 in order to attenuate extraneous interference signals, whereas adiode 41 (typically a type 1N90) is connected in shunt around theseresistors between switch 36 and the base element of transistor 15. Thefunction of diode 41 is that of a protective element shunting leakagecurrent from transistor 15, which sometimes exists in the case of a Getransistor but is usually not a problem where an Si transistor isemployed. Such a leakage current interferes with forceful turn-off oftransistors at the input shunting resistors; however, the difficulty canalso be cured by utilizing a 3 v. turn-off reverse bias as analternative if desired.

Yet another signal input which is frequently encountered is thatillustrated by FIG. 3C, utilizing a steady D.-C. signal current drawnfrom lead 11 via a branch conductor 43 incorporating resistor 44(typically 7.5K ohms) and switch 45, which is retained normally open bymechanical connection 46, shown in broken line representation, at alltimes when the point monitored is in normal behavior, and, conversely,is brought to closed circuit when the point monitored goes abnormal.Again, a positive polarity transistor biasing signal is applied viaresistors 31 and 32" (each typically 3.9K ohms) and resistor 44connected in series one with the other between branch conductor 43 andthe base element of transistor 15, capacitor 40' bridging lead 11 andthe resistor midpoint being identical in value and purpose withcapacitor 40 of FIG. 3B.

The operation of the basic lock-in annunciator of FIG. 1 is the sameregardless of the nature of the input signal circuit. Thus, impositionof a negative polarity signal, either in the form of a relativelytransient pulse or a prolonged D.-C. steady current via a specific inputcircuit such as one of those described, into the base element oftransistor 15, signifying the existence of abnormality at the pointmonitored, biases 4-layer diode 14 and transistor 15 to conductivestate. This establishes relatively heavy current passage through thefirst branch circuit, with consequent illumination of red lamp 16 fromfull darkness to full brightness. The passage of current exceeds theminimum holding current of 4-layer diode 14, which thereafter maintainslamp illuminating current flow through the first branch circuit.

Simultaneously, referring to FIG. 1, a transfer of voltage fromcapacitor 22 back-biases diode 21 and forward biases 4-layer diode 19,thereupon exceeding its threshold voltage value, thereby initiatingheavy current conduction therethrough, so that lamp illuminating currentcontinues to be supplied through green acknowledgement verification lamp2%] for so long as manually operated switch 25 remains closed.

When the point monitored is restored to normality, either by correctiveaction taken by personnel in response to the warning given by theannunciator or in the absence of any human intervention whatever, acorresponding signal is delivered by input circuit 16, which biasestransistor 15 to its non-conductive state. This halts all current flowthrough the first branch circuit and, of course, red lamp 16 immediatelyreverts to its nonilluminated state; however, this has no effect on thesecond branch circuit, since capacitor 22 is effective in the lock-inembodiment of this invention solely to turn on the current in the secondbranch circuit but not to turn it off. Accordingly, illumination ofgreen lamp persists until manual switch 25 .is opened by an attendant,who is instructed to take this action only after taking cognizance ofthe fact that an abnormality has occurred at the point monitored.

It frequently happens that the abnormality at the point monitoredconsists of one or more brief duration incidents Which operatesuccessively to' switch the first branch circuit on and off in sequence.Since the second branch circuit responds to each switching on of thefirst branch circuit, the green acknowledgement verification lamp 20retains the information that an anomaly has occurred until cleared byopening of switch 25, or switches back on subsequent to any givenacknowledgement if the alarm condition repeats, thereby preservinginformation by a lock-in type action completely independent of the firstbranch circuit.

The operation of the basic non lock-in annunciator embodiment of FIG. 2is in all respects the same as that of the lock-in embodiment, exceptthat capacitor 25 is, in this instance, located past transistor 15 ofthe first circuit branch and is, in addition, of much larger size thancapacitor 22, so that it is operative also to extin uish current flowthrough the second branch circuit (by effectively momentarily reducingthe current flow to switching diode L9). The larger size of capacitor 26as compared with capacitor 22 is to afford the somewhat larger R-C timeconstant required to effect turn-off of the solid state diode i19,turn-on being inherently significantly faster, as conducted with theembodiment of FIG. 1. Thus, acknowledgement verification lamp 20 revertsto its nonilluminated condition simultaneously with switch off of redalarm indication lamp 16. Nevertheless, this embodiment still providesan acknowledgement facility operable at all times in the same manner asfor the embodiment of FIG. 1 prior to return to normality of the pointbeing monitored.

The signal provided by the second branch circuit is, especially with thelock-in design, exceedingly important, in that it, in effect,constitutes the memory that an abnormal condition has, in fact, existedat the point monitored, even though that abnormality may have been ofonly very brief duration, and thus have escaped notice so far as thetransient illumination of the red lamp of the first branch circuit wasconcerned. It is, therefore, desirable to provide a second green lamp inshun-t with the first as a reserve standf'oy should the first green lamp\burn out or otherwise fail. In addition, audible alarm and flashingillumination of the green acknowledgement verification l-amp are verydesirable auxiliary features in order to better gain the notice of anattendant, and all of these features are shown in FIGS. 4 and 5 takentogether. Although the embodiments of annunciator per se portrayed inFIG. 4 are dififerent from those of FIGS. 1 and 2 in yet anotherrespect, namely, the substitution of a diode for the transistor as theelectronic blocking means in the first branch circuit, it will beparticularly understood that this has no bearing whatever on the choiceof alarm presentation auxiliaries. Such auxiliaries are completelyapplicable to all other embodiments of the invention, including those ofFIGS. 1 and 2, it being understood that it is then convenient torelocate manual switch 25 (or 25') so that it will simultaneouslydiscontinue any additional alarms co-oper-ating with the acknowledgementverification lamp of the second branch circuit.

Referring to FIG. 4, there are shown two independent annunc-iator unitsconnected across common D.-C. supply leads 11 and 12, the left-hand unitof which is of the lock-in type, whereas the right-hand unit is of thenon lock-in type, this choice of representation having been made toconserve drawing requirements.

When diodes are used instead of transistors in the first branch circuit,signal input is restricted to the pulse type hereinbefore elaboratedgenerally with respect to FIG. 3A, with the difference that theabnormality warning ON signal and the abnormality discontinuance OF'Fsignal must now be applied at different locations in the first branchcircuit. Any disadvantage resident in this fact is cured by the latitudeafforded the designer in choice of signal polarity and voltage magnitudeas well as freedom or" place of signal imposition, which will beunderstood by persons skilled in the art. For purposes of representationsolely, negative polarity ON signals and positive polarity OFF signalsare hereinafter described as the circuit actuation agencies.

Referring to FIG. 4, all branch circuits are shown as provided with theidentical current-stable, negative resistance switching elements,conveniently in the form of 4-layer diodes (all typically 415 -28 types)14", 19, 14, and 19', corresponding to 14, 19 and 14, 19', and also withdiodes 21" and 21", identical with 21 and 21, respectively, andindication lamps 15", 20" and 16", 20' identical with lamps 16, 20 and'16, 20', respectively, of FIGS. 1 and 2. However, diodes 49 and 49(typically type SR1692) are substituted for the transistors 15 and 15',respectively, of the embodiments of FIGS. 1 and 2, requiring impositionof the current-limited negative polarity ON pulse (typically -80 v. 28ma.) via conductor 50 (or 5'0) connected into the first branch circuitbetween switching element 14" (or 14") and diode 49 (or 4 9). Similarly,the positive polarity OFF pulse of magnitude imposing effectively zerovolts across the switching element is necessarily introduced viaconductor 51 (or V 51 connected into the first branch circuit betweendiode 49 (or 49') and the red alarm indication lamp 16" (or 16"). In thecase of the non lock-in embodiment of FIG. 4, the OFF signal pulse isapplied simultaneously to both branch circuits via a bridging conductor52 provided with diodes 53 and 53' (typically type SRl692) in theindividual halves reserved to the first branch circuit and the secondbranch circuit, respectively, which are coupled one to the other in bothembodiments by an upper bridging conductor 54 (or 54') provided withcapacitor 55 (or 55) typically of 0.01 mfd. size.

As previously mentioned, a reserve green acknowledgement verificationlamp 20a (or 20a) is provided in shunt connection with lamp 20" (or 20")in the second branch circuit, and audible and flashing signalauxiliaries are added by way of improving the alarm presentations.

Thus, referring to FIGS. 4 and collectively, an audible bus 58 ispreferably provided for servicing a plurality of annunciator units, theconnection of only one, e.g., a lock-in embodiment incorporating astandby reserve green lamp, such as the left-hand unit of FIG. 4, beingportrayed in FIG. 5 by detailing solely the connections to the greenlamps and 20a". The second branch connections to bus 58 are made in allcases through a resistor 59 (or 59), typically 330 ohms, whicheffectively interposes enough resistance in series with lamps 20" and20a" to bring them to approximately half brilliance during alternatehalf cycles of operation of the flasher hereinafter described.

The remaining circuit completion connection for the second branchcircuit is via diode 60 (or 60), typically a type SR1692, and conductor61 (or 61') running to flasher bus 64. Since, in most cases, it isdesired to effect acknowledgement of a plurality of points monitoredsimultaneously, audible bus 58 is provided with a common pushbuttonswitch 65, and flasher bus 64 is similarly provided with a commonpushbutton switch 66 ganged for simultaneous operation with switch bythe mechanical connection indicated schematically in broken linerepresentation at 67. These switches together correspond functionallywith manual switches 25 and 25 of FIGS. 1 and 2. All pushbutton switchesare shunted by individual resistors 68 (typically 100K ohms each) whichrestore the voltage across any current-stable, negative resistanceswitching elements, such as the 4-layer diode 19, and its counterparts,after disruption of the heavy current supply path produced by opening ofthe switches 65,. 66 and their counterparts. This is a precautionagainst possible spurious switching action on the part of these diodeswhich can sometimes result from a rapid voltage rise thereacross in theabsence of current-limiting such as provided by these resistors.

The audible alarm, indicated generally by block 70 is a conventionalrelay or voltage controlled oscillator, which is provided with avoltage-limiting diode 71 connecting audible bus 58 with the common bus12. Diode 71 is shunted by resistor 72 (typically 100 ohms), so thatreturning current flow developing a signal in excess of about /2 v.actuates the audible alarm. It might be mentioned that diode 71 limitsthe voltage drop to about one volt, no matter how many green lamps 20",20a", or their counterparts are on, whereas resistor 72 averts actuationof audible alarm 70 by any minor leakage currents which could otherwisecause the audible alarm to sound.

Flasher 73 connected between flasher bus 64 and common bus 12 is aconventional motor-driven cam-operated switch, or its solid-stateequivalent, which, when its contact 73a is closed, shunts current aroundresistor 59 via diode 60 through the flasher, which operationrepetitively dims lamps 20 and 20a" during each half cycle of operationof flasher 73. It will be understood that flasher 73 coincidentally alsomodulates the current supplied to audible alarm 70, so that the audiblealarm goes on and off at the flashing rate (typically, one cycle/sec),which is desirable. Finally, the diodes corresponding to diode 60constituting components of neighboring annunciator units isolate each ofthese annunciators from concurrent operation with thosemonitoring'points in alarm.

FIG. 5 shows additional circuitry provided for yet other optionalauxiliaries, such as First-On indication and Ring Back; however,description of these features is postponed until the related circuits ofFIGS. 6 and 7 are hereinafter taken up.

Turning now to the operation of the specific embodiment of FIG. 4, theintroduction of a negative polarity ON pulse via lead 50, signifying theexistence of an abnormal state in the point monitored by theannunciator, immediately increases the effective voltage drop acrossswitching diode 14 and, the limiting threshold of diode 14" beingexceeded, initiates heavy current flow through the first branch circuit,thereby illuminating the red alarm indication lamp 16". The ON pulsesimultaneously develops a charge within capacitor 55 via conductor 54which immediately transfers a voltage thereacross, effectivelyincreasing the voltage drop across switching diode 19", exceeding thevoltage threshold thereof and initiating heavy current flow through thesecond branch circuit. This illuminates green lamps 20 and 20a, theacknowledgement verification lamps, by completion of the circuit tocommon bus 12 via both audible'bus 58 and flasher bus 64, as best shownin FIG. 5. Since the latter'circuit path is cyclically interrupted byopening of motor-driven switch 73a within flasher 73, there issimultaneously obtained both flashing illumination of green lamps 20"and 20a" and a fluctuating audible alarm signal emitted by audible alarm70, calling the attendants attention to the fact that an abnormality hascome into existence at the particular point serviced by the annunciator.In usual practice the attendant will immediately acknowledge that he hasbecome aware of the existence of the abnormality by momentary opening ofthe normally closed ganged pushbutton switches 65 and 66, therebydiscontinuing both the audible alarm and the flashing illumination oflamps 20" and 20a", whichrevert to their non-illuminated state. However,if the abnormality persists past the time of acknowledgement, red alarmindication lamp 16" remains illuminated. It is only when further actionis taken by the attendant in correction of conditions causing theabnormality that a positive polarity OFF pulse is transmitted to thefirst branch circuit via conductor 51. This positive pulse, byback-biasing diode 49, effectively reduces the. current flow throughswitching diode 14" to below the minimum holding current of this diode,thereby switching the diode off and discontinuing current flow in thefirst branch circuit, so that red alarm indication lamp 16" (FIG. 4)goes olf.

Turning now to FIG. 6, it is frequently desirable to incorporate a RingBack auxiliary with lock-in type annunciators, and this is readilyaccomplished with the invention design. Ring Back is obtained byproviding an independent branch circuit connected in parallelrelationship to the first and second branch circuits of the basicannunciator per se across D.-C. supply leads 11 and 12, connection withthe latter lead being conveniently made via the common flasher bus 64shown in FIG. 5 and a separate common Ring Back audible bus 75.

The individual components'connected in series circuit in the independentRing Back branch circuit correspond generally to those hereinbeforedescribed for the basic annunciator circuit and consist of acurrent-stable, negative resistance switching element, such as the4-layer switching diode '77 (typically a type 4E80-28), a Ring Backindication lamp 78 (typically a type No. 1835 identical with lamps 16,2t) and their counterparts hereinbefore described), which can be ofdistinctive amber color, and two parallel-connected diodes, 79 and 8t)(typically each of type SR1692), completing the circuits to buses 64 and75, respectively. Again, to obtain cyclic-a1 dim-to bright operation ofRing Back lamp 78, a resistor 81 (typically of 680 ohm value) isinterposed between diode 8t) and Ring Back audible bus 75. Since acompletely independent Ring Back audible signal of distinctive pitch isdesirable to distinguish audibly between the eration.

of the Ring Back audible alarm is provided by normally closed Ring Backacknowledgement pushbutton switch S7 interposed in bus 75 ahead ofaudible alarm 84. Switch 87 is ganged for simultaneous operation throughmechanical connection 88 with a companion normally closed pushbuttonswitch 89, corresponding to switch 66, interposed in flasher bus 64 and,again, shunt resistors 68 are connected across these switches to avertany spurious operation of switching diode 77.

, Co-ordination of the independent Ring Back circuit with the basicannunciator circuit is obtained by coupling with the annunciator firstbranch circuit, the red alarm indication lamp 16' of which is shown inbroken line representation in FIG. 6, via conductor 91 having interposedtherein capacitor 92 (typically 0.01 mfd. size), and with the secondbranch circuit by conductor 93 connected just ahead of greenacknowledgement verification lamps 20 and 20a, also shown in broken linerepresentation. Conductor 93 has interposed therein Zener diode 96(typically a 56 v. type IN732), and, preferably, a currentlimiting R-Cnetwork consisting of parallel-connected resistor 97 (typically K ohms,/2 watt) and capacitor 98 (typically 0.1 rnfd. size). The purpose ofresistor 97 is to limit D.-C. current flow while the purpose ofcapacitor I 98 is to pass A.-C. current flow through Zener diode 96,

Acknowledgement of Ring Back is accomplished simply by the attendantsmomentary opening of the normally closed Ring Back acknowledgementpushbutton 87 (FIGS. 5 and 7A) together with its gang-associated switch89 in flasher bus 64.

Yet another optional auxiliary which is frequently advantageousapplicableto both lock-in and non lock-in annunciators, is that ofFirst-On indication, a preferred embodiment of sub-circuit for which isshown in FIG. 7. This entails provision of an independent branch circuitreversed to First-On indication at each point monitored, which branchcircuit is connected in generally parallel relationship with respect tothe annunciator proper first that Ring Back lamp 78 come intoillumination when red alarm indication lamp 16 turns off, providing,however, that the attendant has already acknowledged the existence of ananomaly in the monitored point by having previously opened thepushbutton acknowledgement switch 65. The reason for this is that it isordinarily not desirable to obtain Ring Back action for points onlymomentarily in alarm. Accordingly, concerted action is called for byboth the first branch circuit and the second branch circuit of theannunciator applicable to the independent Ring Back circuit.

The operation of the Ring Back auxiliary involves the transfer of avoltage across capacitor 92 incident to the extinction of red alarmindication lamp 16 which creates a voltage drop across switching diode77 exceeding its threshold level, thereby initiating heavy current flowthrough diode 77 into the Ring Back branch circuit. However, if theannunciator second branch circuit is in its ON state, as evidenced bycontinued illumination of green acknowledgement verification lamps 20and 20a prior to abnormality acknowledgement by the attendant throughoperation of switches 65-66, Ring Back switching diode 77 will beshunted by the existence of a voltage dropping path through lamp 78,Zener diode 96, conductor 93 and the annunciator second branch circuit.Under these circumstances switching diode 77 will be inhibited fromswitching ON and Ring Back lamp 78 will remain unilluminated.

The foregoing operation is clarified further by reference I to FIG. 7A,4-layer diode 19 upon heavy current flow therethrough making line 93swing to a high positive voltage reversing the bias on Zener diode 96,to drive it into high negative conduction. The high negative currentthus impressed through 4-layer diode 77 prevents its op- Thereafter,upon ringback, Zener diode 96 is forwardly biased so as to pass littlecurrent, and capacitor 92 transfers a negative pulse to trigger on4-layer diode 77.

and second branch circuits, as well as' with any other auxiliaries, suchas the Ring Back hereinbefore described, across D.-C. supply lead 11 onthe one hand and a First-On acknowledgement bus 101 connected in turn tothe common bus .12- Referring especially to FIG. 7, the independentFirst-On branch circuit incorporates in series connection individualcomponents identical with those of the annunciator first and secondbranch circuits, including diode 102 (typically a type SR1692), aFirst-On indication lamp 103 of any desired color (e.g., white),preferably of the same type as lamps 16, 20, 20a and their counterpartshereinbefore described, and a current-stable, negative resistanceswitching element, such as 4-layer switching diode 104 (typically a type4E80-28 identical with the switching diodes 14,19 in-the annunciatorproper). The First-On branch circuit is coupled to the annunciator firstbranch circuit, indicated fragmentarily in broken line representation,via conductor 105 provided with capacitor 106 (typically 0.01 mfd.size).

Since all First-On auxiliaries are connected in a v common circuitarrangement which would illuminate the lamps in all of themsimultaneously, and thus lose the First-On indication which is the solefunction of the auxiliary, each must be provided with means positivelypreventing such a contingency. This necessitates the use of individualshunting circuits around each of the switching diodes 104 which are ofthe same design as those hereinbefore described for the Ring Backauxiliary of FIG. 6. Thus, there is provided a Zener diode 108preferably in series circuit with a current-limiting R-C network,incorporating resistor 109 (typically, 5K ohm size) parallel-connectedwith capacitor 110 (typically, 0.1 mid. size), connected to the First-Onbranch circuit between lamp 103 and switching diode 104. The otherterminal of the shunting circuit is connected to a common First- Onclamp bus 111, to which all other First-On circuits are similarlyconnected. Clamp bus 111 can either be floating, as shown in FIG. 7, inthe sense that no connection whatever with common bus 12 is required, orit can be connected to the latter through a rather large value resistor(typically K ohms).

By way of explaining the operation, it is assumed that the monitoredpoint serviced by the First-On unit shown in FIG. 7 goes abnormal. Thealarm condition is immediately signaled by the annunciator first branchas hereinbefore described, which imposes a charge of polarity andmagnitude on capacitor 106 via lead exceeding the threshold level ofswitching diode 104, thereupon causing heavy current flow through theFirst-On cir-- cuit, together with illumination of the First-Onindication lamp 103. The attendant acknowledges receipt of theinformation by momentarily opening normally closed acknowledgementswitch 100 (FIG. 5) interposed in the First-On acknowledgement bus 101,which restores the alarm received from its monitored .point, it is, ofcourse, necessary that the particular First-On circuit of 'FIG. 7.

remain inactive. This operation is assured by Zener diode 108, whichprevents clamp bus 111 from ever becoming more than a few volts positivewith respect to common bus 12, when a neighboring First-On unit, all ofwhich are connected to the same clamp bus 111, is turned on.Accordingly, the shunting action of Zener diode 108 with respect toswitching diode 104 is effective to prevent the latter from everreaching the 80 v. threshold which is necessary to produce switchingaction, and no two First-On units can thus ever be actuatedsimultaneously, provided, of course, that there exists a few millisecs.delay between any two alarm incidents.

As most clearly seen in FIG. 7A, capacitor 106 switches on 4-layer diode104, Zener diode 108 being highly reverse biased so as to pass a highnegative current to clamping bus 111. This high negative current isdrawn through 4-layer diode 104 and Zener diode 108 of the right-handmodule, as well as the counterpart diodes in all other modules connectedin the same system, thereby reverse biasing all other 4-layer diodescorresponding to 104, preventing their subsequent conduction.

Turning now to FIGS. 8A and 813, it is entirely practicable tosubstitute a neon lamp (typically type LNE48) in the dual capacity of areplacement for both the indication lamp and the switching element ofeither the first or second branch circuits (or both of them) in any ofthe annunciator embodiments hereinbefore described.

A preferred pulse-actuated design of first branch circuit is that shownin FIG. 8A wherein the B+ supply lead is denoted 11a, carried at ahigher voltage level (typically 105 v.) than its previously describedcounterpart 11 to accommodate the characteristics of the neon lamp 115.As will become clear from the following description, lead 122,maintained at typically +150 v., is necessary to the signal input, sothat it is convenient to derive the +105 v. supply of the D.-C. supplylead pair from lead 122 by connection with it through resistor 116.Voltage dropping resistors 116 (typically 10K ohms value) and 117(typically 6.8K ohms value) are respectively provided ahead of, andafter, lamp 115, thereby establishing convenient base levels forimposition of the ON pulse (typically v.), which is the signalsignifying the existence of an abnormal state in the point monitored,via lead 119, and the OFF pulse (typically +50 v.), which is the signalsignifying restoration of the point monitored to normal value, via lead120. In this annunciator design the connection with the associatedsecond branch circuit is via conductor 121, provided with the usualcoupling capacitor (not shown), represented in broken linerepresentation in FIG. 8A.

Since lead 11a is the common B+ bus for a plurality of annunciatorunits, it is necessary to isolate each individual first branch circuitby a diode 118 (typically a type SR1692), and to also provide a clampingZener diode 124, only .one of which latter is required for a pluralannunciator set up, connected from the back side of any specific diode118 to common bus 12a. With this provision, lead 110 is effectivelybiased at +105 v., which is a very satisfactory B+ level for thisembodiment.

In operation, the negative polarity ON pulse imposes a voltage acrossneon lamp 115 SUfl'lClfiDt to fire it, which is a substitute for theswitching role previously performed by switching diode 14 and itscounterparts, at the same time illuminating the lamp, so that anindication of abnormality existence is given equivalent to that of redlamp 16, FIG. 1, or its counterparts previously described. Also, whenthe abnormality is rectified, or disappears, the OFF pulse imposed vialead 120 effectively lowers the voltage drop across lamp 115, whichthereupon goes out, discontinuing its alarm indication. In thisconnection it should be noted that neon lamps of the type describedsustain conduction, once fired, at a potential level of to v., so thatthe lead 11a at v. potential is entirely ample to keep lamp inillumination, once it is turned on. Turn off of lamp 115 requires thedevelopment of a voltage drop in the lamp anode circuit, so that lead122 at +150 v. merely serves as the necessary current supply lead, viaload resistor 116, required on the part of the signal input to efiectthis operation.

It will be understood that a first branch circuit utilizing a neon lampas described for the embodiment of FIG. 8A can be readily combined toform a complete annunciator unit according to this invention with asecond branch circuit of any of the designs hereinbefore described or,alternatively, the second branch circuit can utilize a neon lamp in thesame general manner as that taught for FIG. 8A.

Thus, referring to FIG. 8B, the second-branch circuit can consist simplyof an acknowledgement verification lamp 127 (again typically a typeLNE4S) connected, on the one side, to the 13+ lead 111! through a diode128 (typically type SR1692) and on the other side through acurrent-limiting resistor 129 (typically 6.8K ohms) to a commonacknowledgement bus 130 provided with an acknowledgement switch such aspushbutton switch 100, FIG. 5 (which, in this case, should not beprovided with a shunting resistor 53), in turn connected to a common bus12, which latter two components are not shown in FIG. 83. Finally, thesecond branch circuit is coordinated with the first branch circuit by aconductor 131. having interposed therein a capacitor 132 (typically 0.01mid. size), thereby completing the assembly of a basic lock-in typeannunciator unit.

Operation is in all respects similar to that of the embodimentshereinbefore described, acknowledgement verification lamp 127 serving inthe same dual capacity as already explained for lamp 115 of the firstbranch circuit, so that lamp 127 fires practically simultaneously withlamp 115 upon transfer of a voltage from capacitor 132 responsive toreceipt by the first branch circuit of an ON signal pulse input via lead119 signifying existence of an alarm condition at the point monitored.

Lamp 127 thereafter continues in illumination until the attendantsignifies receipt of the information by momentary opening of theacknowledgement switch (not shown) interposed in circuit withacknowledgement bus 130. The annunciator circuit is thereupon restoredto its original state, ready for handling of any new alarm incidentswhenever they should occur.

The detailed circuitry for two basic lock-in type annunciators employingneon lamps in the dual capacity described, and provided with audible busand flasher bus auxiliaries as hereinbefore described for otherembodiments, is shown in FIG. 9, the left-hand annunciator beingpulse-actuated whereas the right-hand annunciator is steadycurrent-actuated.

Components in the pulse-actuated embodiment of FIG. 9 are represented bythe same reference numerals as employed for their counterparts of FIGS.8A and 813, except with a prime appended, and the identity is believedamply clear, although certain slight alterations were made toaccommodate the auxiliaries and the differing signal inputs. Thus, theresistor corresponding to resistor 129, FIG. 8B, is now effectivelysplit into two parts (each, typically, of 6.8K ohm value), the first,129a, being connected between acknowledgement verification lamp 127' andconductor 133 having in series with it diode 134, which establishescircuit with flasher bus 130", whereas the second, resistor 12%, isinterposed after resistor 129a in the circuit path running to theaudible bus 130. The operation of this embodiment of annunciator isexactly as hereinbefore described with respect to FIGS. 8A and 8B, andhence is not repeated.

The right-hand annunciator unit employs normally closed contactactuation in the signal input, being in this respect similar to thesignal input portrayed in FIG. 313, so that the existence of an alarmcondition in the point monitored is signaled by the opening of switch141 under mechanical actuation denoted schematically in broken linerepresentation at 142. The first branch circuit, connected across D.-C.supply leads 122 and 12a, consists 13 of neon alarm indication lamp 145(typically a type LNE48) in series with resistor 146 (typically 6.8K ohmvalue). This connection to the higher voltage (i.e., +150 v. bus 122')is necessary in order to obtain firing of the alarm indication lamp 145,because, while +105 v. derived from supply lead 11a is eflfective as aneon lamp illumination-sustaining voltage, it is below firing level.

Switch 141 is connected from a point between resistor'144 to audible bus130' and flasher bus 130".

In operation, switch 141 remains closed in the absence of an abnormalcondition at the point monitored, effectively shunting alarm indicationlamp 145, which therefore remains unilluminated. When an abnormalityarises, switch 141 is opened by mechanical actuator 142, thereuponimposing full voltage across lamp 145, firing it and applying, throughcoupling capacitor 132", a back bias on diode 128" sufiicient to firethe acknowledgement verification lamp 127", which latter then conductscurrent to both the associated audible and flasher alarm buses 130 and130 as hereinbefore described for the embodiments of FIGS, 4 and 5.

When switch 141 recloses upon restoration of the point monitored tonormality, lamp 145 is shunted out and therefore goes dark, whereas lamp127" remains illuminated until the attendant opens an acknowledgementswitch (notshown) identical in all respects with those described forFIGS. 4 and 5. The operation cycle then stands completed until a newanomaly arises at the point monitored.

It will be understood that the annunciator embodiments utilizing neonlampsas both visual indicators and switching elements can, if desired,also be provided with any of the other auxiliaries as well, includingRing Back and First-On.

Yet another lock-in type annunciator employing dual capacity neon lampsas visual indicators, together with pulse signal input, is that shown inFIG. 10. Since the second branch circuit of this embodiment is identicalin all respects with the second branch circuit of the righthandembodiment of annunciator shown in FIG. 9, the various componentsthereof are denoted by the same reference numerals.

In this design the first branch circuit is connected across the +105 v.bus 11a and bus 12a as the D.-C. supply leads, and incorporates thealarm indication neon lamp 151 (typically a type.LNE48), P-N-Ptransistor 152 (typically type 2N598A) and resistor 3 (typically 6.8Kohms value). The base element of transistor 152 is connected to bus 12athrough series-connected resistors 155 and 156 (each typically 3.9Kohms), and the signal input is applied intermediate these resistors inthe form of a negative polarity ON pulse (typically 50 v.) suppliedthrough lead 159 and a positive polarity OFF pulse (typically +50 v.)supplied through lead 160.

In operation, the existence of abnormality in the point monitored issignaled by the delivery of the negative polarity ON pulse via lead 159to the base element of transistor 152, and the transistor thereupondevelops a large enough voltage drop to fire alarm indication lamp151,1.hus illuminating it. Simultaneously, a back bias is imposedthrough coupling capacitor 132" on diode 128", second branch circuit, todevelop firing voltage across acknowledgement verification lamp 127",which imme- A ca-- A positive polarity OFF pulse of magnitudeapproximately +50 v., delivered via lead 160 responsive to restorationof the monitored point to normality, at once reduces the voltage appliedacross lamp 151, and the lamp goes dark, completing the operation cycleand plac-, ing the annunciator unit once again in serveillance service.

Still another embodiment of first branch circuit, which is exceedinglysimple in design, is that shown in FIG. 11. This design requires use ofa normally open contact type signal input, which is not generallyregarded with favor by persons skilled in the art, because an accidentalbreak in the circuit, or oxidation at the. contacts barring currentpassage therethrough, are, of course, both indistinguishable from a lampindication corresponding to a safe state for the point monitored.

In any case, such a first branch circuit consists simply of an alarmindication lamp 16b connected through a normally open switch acrossD.-C. supply leads 11b and 12b. Alarm condition for the point monitoredis signaled by closure of switch 135 through the agency of mechanicalconnection 136, which closure must, of course,

' the usual manner via conductor 137 having interposed in seriestherewith a capacitor 138 (typically 0.01 mid. size). The operation ofthis embodiment is in all respects similar to that of the others alreadydescribed and is, therefore, not detailed herein.

While this invention has been illustrated by circuits employing P-N-Ptype transistors, the use of the N-P-N type is equally practicable,provided, of course, that the several circuit connections are modifiedas required by the polarity reversal thereby involved, Moreover, it is,of course, possible to utilize a single, dual-filament lamp insubstitution for the paired individual alarm indication andacknowledgement verification lamps hereinbefore described, reserving onefilament exclusively to one function and the other filament to the otherfunction. In the latter case, distinctiveness in the illumination wouldrequire steady operation of one filament andflashing operation of theother, or something equivalent, and, also, modification of intracircuitconnections would be necessary, all as understood in the art, but thebasic principles and circuits hereinbefore disclosed are all fullyapplicable.

From the foregoing, it will be understood that this invention can bevaried in numerous respects within the skill of the art withoutdeparture from its essential spirit,

and it is therefore intended to be limited only within the.

scope of the appended claims.

What is claimed is:

1. An electrical annunciator circuit comprising in combination a D.-C.supply, a first electronic bistable switching branch circuit and asecond electronic bistable switching branch circuit connected inparallel circuit relation: ship one to the other across said D.-C.supply, said first electronic, bistable switching circuit being providedwith an alarm indication lamp together with an alarm indication controlmeans consisting of a solid state electronic blocking means and acurrent-stable negative resistance switching element connected in serieselectrical circuit with said alarm indication lamp, said electronicblocking means having applied thereto a-fixed preselected polarity biasof magnitude such that the voltage difference between t the side of saidD.-C. supply having said preselected polarity and said bias does notexceed the switching threshold of said switching element and whereinsaid electronic blocking means has applied to it, first, said signalsignifye ing the existence of an abnormal state in a point monitored ofsaid preselected polarity and a voltage magnitude developing a firstvoltage drop across said switching element exceeding said switchingthreshold of said switching element, thereby actuating said switchingelement to its ON state drawing electrical current from said D.C. supplythrough said first electronic bistable switching branch circuit toestablish a distinctive illuminated state of said alarm indication lampand, second, said signal signifying the restoration of said pointmonitored to normal state of polarity opposite from said preselectedpolarity and a voltage magnitude reducing the current flow through saidswitching element below the holding current value of said switchingelement, thereby actuating said switching element to the OFF statehalting said drawing of electrical current through said firstelectronic, bistable switching branch circuit, thus disestablishing saiddistinctive illuminated state of said alarm indication lamp, said secondelectronic, bistable switching branch circuit being provided with anacknowledgement verification lamp together with acknowledgementverification lamp switch on means establishing a distinctive illuminatedstate of said acknowledgement verification lamp responsive to theestablishment of said distinctive illuminated state of said alarmindication lamp, and manually operated means disestablishing at willsaid distinctive illuminated state of said acknowledgement verificationlamp.

2. An electrical annunciator circuit according to claim 1 wherein saidelectronic blocking means is a transistor operating in the switchingmode to which said signal signifying the existence of an abnormal statein said point monitored and said signal signifying the restoration ofsaid point monitored to normal state are applied via the base element ofsaid transistor.

3. An electrical annunciator circuit according to claim 1 wherein saidalarm indication lamp control means consists of a transistor aselectronic blocking means and a current-stable, negative resistanceswitching element connected in series electrical circuit with said alarmindication lamp, provided with signal input means consisting of anindependent branch circuit made up of a series-connected resistor andsingle-pole, single-throw switch connected in parallel circuitrelationship with said first electronic, bistable switching branchcircuit and said second electronic, bistable switching branch circuitacross said D.-C. supply and, via a cross connection running from apoint between said resistor and said switch, to the base element of saidtransistor, said switch being actuated to a first uniquie positionresponsive to the existence of an abnormal state in a point monitoredconnecting said base element of said transistor in circuit with the sideof said D.-C. supply having a preselected polarity and a voltagemagnitude applying said signal signifying the existence of said abnormalstate in said point monitored by development of a "oltage drop acrosssaid switching element exceeding said switching threshold of saidswitching element, so as to actuate said switching element to its ONstate drawing electrical current from said D.-C. supply through saidfirst electronic, bistable switching branch circuit thus establishingsaid distinctive illuminated state of said alarm indication lamp, andsaid switch being actuated to a second unique position responsive to therestoration of said point monitored to normal state connecting said baseelement of said transistor in circuit with the side of said D.-C. supplyhaving a polarity opposite from said preselected polarity and a voltagemagnitude applying said signal signifying said restoration of said pointmonitored to normal state by reduction of the current flow through saidswitching element, so as to actuate said switching element to the OFFstate halting said drawing of electrical current through said firstelectronic, bistable switching branch circuit, thus disestarblishingsaid distinctive illuminated state of said alarm indication lamp.

4. An electrical annunciator circuit according to claim 1 wherein saidalarm indication lamp control means consists of a diode as electronicblocking means and a current-stable, negative resistance switchingelement connected in series electrical circuit with said alarmindication lamp, said signal signifying the existence of an abnormalstate in said point monitored is of a first preselected polarity andvoltage magnitude introduced at a location in said first electronic,bistable switching branch circuit back-biasing said diode andsimultaneously raising the voltage across said switching element to alevel actuating said switching element to its ON state drawingelectrical current from said D.-C. supply through said first electronic,bistable switching branch circuit to thereby establish said distinctiveilluminated state of said alarm indication lamp, and said signalsignifying the restoration of said point monitored to normal state is ofa second preselected polarity and voltage magnitude introduced at alocation in said first electronic, bistable switching branch circuitreducing current fiow through said switching element below the holdingcurrent value to thereby actuate said switching element to its OFF statehalting said drawing of electrical current through said firstelectronic, bistable switching branch circuit and thus disestablish saiddistinctive illuminated state of said alarm indication lamp.

5. An electrical annunciator circuit according to claim 1 provided witha FirsbOn auxiliary consisting of an independent electronic, bistableswitching branch circuit connected in parallel circuit relationship withrespect to said first electronic, bistable switching branch circuit andsaid second electronic, bistable switching branch circuit across saidD.-C. supply, said independent electric, bistable switching branchcircuit being provided in series electrical connection with a diode, aFirst-On indication lamp, a current-stable, negative resistanceswitching element and a normally closed, manually operated First-Onacknowledgement switch, said independent electronic, bistable switchingbranch circuit being coupled via a capacitor to said first electronic,bistable switching branch circuit and via a Zener diode connected inshunt with said switching element to a First-On clamping bus, said Zenerdiode providing a shunting back-circuit with respect to said switchingelement closed by previous unacknowledged actuation of any otherFirst-On circuits tied to said clamping bus, and said capacitortransmitting a signal of preselected polarity and voltage magnituderesponsive to said establishing of said distinctive illuminated state ofsaid alarm indication lamp back-biasing said diode and thereby raisingthe voltage imposed across said switching element to a level actuatingsaid switching element to On state drawing current through saidindependent electronic, bistable switching branch circuit to therebyestablish a distinctive illuminated state in said First-On indicationlamp subject, however, to the concomitant existence of said Zener diodein non-shunting state. i

6. An electrical annunciator circuit according to claim 1 provided witha Ring Back auxiliary consisting of an independent electronic, bistableswitching branch circuit connected in parallel circuit relationship withrespect to said first electronic, bistable switching branch circuit andsaid second electronic, bistable switching branch circuit across saidD.C. supply, said independent electronic, bistable switching branchcircuit being provided in series electrical connection with acurrent-stable, negative resistance switching element, a Ring Backindication lamp, a diode and a normally closed, manually operated RingBack acknowledgement switch, said independent electronic, bistableswitching branch circuit being coupled via a capacitor to said firstelectronic, bistable switching branch circuit and via a Zener diode tosaid second electronic, bistable switching branch circuit, saidcapacitor transmitting a signal of preselected polarity and voltagemagnitude responsive to said disestablishing of said distinctiveilluminated state of said alarm indication lamp back-biasing said diodeand thereby raising the voltage imposed across said switching element toa level actuating said switching element to ON state drawing currentthrough said independent electronic, bistable switching branch circuitto thereby establish a distinctive illuminated state in said Ring Backindication lamp subsequent to said disestablishment of said distinctiveilluminated state of said acknowledgement verification lamp and theconcomitant disruption of the shunting eflfect of said Zener diodeinhibitory of switching action on the part of said switching element insaid independent electronic, bistable switching branch circuit.

References Cited by the Examiner UNITED STATES PATENTS Re. 24,031 Re.25,214

18 3,029,421 4/1962 Beguin 340213.1 3,081,449 3/1963 Wernlund 340213.1 X3,084,338 4/1963 Mauer et al. 340213.1 3,098,953 7/1963 Herr. 3,107,34910/1963 Sperry 340-2132 3,124,793 3/1964 Foster 340213.2

10 Control Engineering, December 1956 pp. 70-76.

NEIL C. READ, Primary Examiner.

ROBERT M. ANGUS, Assistant Examiner.

1. AN ELECTRICAL ANNUNCIATOR CIRCUIT COMPRISING IN COMBINATION A D.-C.SUPPLY, A FIRST ELECTRONIC BISTABLE SWITCHING BRANCH CIRCUIT AND ASECOND ELECTRONIC BISTABLE SWITCHING BRANCH CIRCUIT CONNECTED INPARALLEL CIRCUIT RELATIONSHIP ONE TO THE OTHER ACROSS SAID D.-C. SUPPLY,SAID FIRST ELECTRONIC, BISTABLE SWITCHING CIRCUIT BEING PROVIDED WITH ANALARM INDICATION LAMP TOGETHER WITH AN ALARM INDICATION CONTROL MEANSCONSISTING OF A SOLID STATE ELECTRONIC BLOCKING MEANS AND ACURRENT-STABLE NEGATIVE RESISTANCE SWITCHING ELEMENT CONNECTED IN SERIESELECTRICAL CIRCUIT WITH SAID ALARM INDICATION LAMP, SAID ELECTRONICBLOCKING MEANS HAVING APPLIED THERETO A FIXED PRESELECTED POLARITY BIASOF MAGNITUDE SUCH THAT THE VOLTAGE DIFFERENCE BETWEEN THE SIDE OF SAIDD.-C. SUPPLY HAVING SAID PRESELECTED POLARITY AND SAID BIAS DOES NOTEXCEED THE SWITCHING THRESHOLD OF SAID SWITCHING ELEMENT AND WHEREINSAID ELECTRONIC BLOCKING MEANS HAS APPLIED TO IT, FIRST, SAID SIGNALSIGNIFYING THE EXISTANCE OF AN ABNORMAL STATE IN A POINT MONITORED OFSAID PRESELECTED POLARITY AND A VOLTAGE MAGNITUDE DEVELOPING A FIRSTVOLTAGE DROP ACROSS SAID SWITCHING ELEMENT EXCEEDING SAID SWITCHINGTHRESHOLD OF SAID SWITCHING ELEMENT, THEREBY ACTUATING SAID SWITCHINGELEMENT TO ITS "ON" STATE DRAWING ELECTRICAL CURRENT FROM SAID D.-C.SUPPLY THROUGH SAID FIRST ELECTRONIC BISTABLE SWITCHING BRANCH CIRCUITTO ESTABLISH A DISTINCTIVE ILLUMINATED STATE OF SAID ALARM INDICATIONLAMP AND, SECOND, SAID SIGNAL SIGNIFYING THE RESTORATION OF SAID POINTMONITORED TO NORMAL STATE OF POLARITY OPPOSITE FROM SAID PRESELECTEDPOLARITY AND A VOLTAGE MAGNITUDE REDUCING THE CURRENT FLOW THROUGH SAIDSWITCHING ELEMENT BELOW THE HOLDING CURRENT VALUE OF SAID SWITCHINGELEMENT BELOW THE CURRENT FLOW THROUGH ING ELEMENT TO THE "OFF" STAGEHALTING SAID DRAWING OF ELECTRICAL CURRENT THROUGH SAID FIRSTELECTRONIC, BISTABLE SWITCHING BRANCH CIRCUIT, THUS DISESTABLISHING SAIDDISTINCTIVE ILLUMINATED STATE OF SAID ALARM INDICATION LAMP, SAID SECONDELECTRONIC, BISTABLE SWITCHING BRANCH CIRCUIT BEING PROVIDED WITH ANACKNOWLEDGEMENT VERIFICATION LAMP SWITCHTOGETHER WITH ACKNOWLEDGEMENTVERIFICATION LAMP SWITCHON MEANS ESTABLISHING A DISTINCTIVE ILLUMINATEDSTATE OF SAID ACKNOWLEDGEMENT VERIFICATION LAMP RESPONSIVE TO THEESTABLISHMENT OF SAID DISTINCTIVE ILLUMINATED STATE OF SAID ALARMINDICATION LAMP, AND MANUALLY OPERATED MEANS DISESTABLISHING AT WILLSAID DISTINCTIVE ILLUMINATED STATE OF SAID ACKNOWLEDGEMENT VERIFICATIONLAMP.